Interesting points and observations from the blog of Dr John Hawks pertaining to the Foramen magnum as an indication of bipedalism…….

“Our results show that locomotion does not influence FM orientation in marsupials, rodents, or strepsirrhines, and that basicranial evolution is a complex phenomenon that must be explored in the context of each taxon’s unique evolutionary and developmental history.”

This is not the first paper to come to this result; Ruth and colleagues cite a number of others who have had similar conclusions either from a comparative or mechanical point of view.

“The obvious question is: What about early hominins? Two genera of Late Miocene and Early Pliocene primates, Sahelanthropus and Ardipithecus, have been argued to show evidence of an orthograde postural repertoire, largely due to their basicranial form, including foramen magnum orientation. For Sahelanthropus there is no otherevidence of posture; for Ardipithecus there is an abundance of postcranial evidence, none of which argues compellingly for an orthograde posture.”

“Our data from all three taxa examined show that locomotion and posture do not influence FM position or orientation, and we conclude that this is likely in hominids as well. Anterior migration of the foramen magnum in early, small-brained hominids likely reflects changes in the relative sizes of the brain’s components (i.e., an expanded neocortex) (Holloway, 1966 and Holloway et al., 2003), and as such is still a useful indicator of the behavior and biology of extinct species. Bipedality, however, should be inferred from the postcranium.” Continue Reading

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